HIGH CONCENTRATIONS OF EXOPOLYMERIC SUBSTANCES IN WINTERTIME SEAICE: IMPLICATIONS FOR CRYOPROTECTION OF DIATOMS AND THE POLAR OCEAN CARBON CYCLE

Exopolymeric substances (EPS) play important roles in various aquatic, porous, subterranean and extreme environments. Only recently has their occurrence in sea ice been considered. Using Alcian blue staining techniques, we observed high EPS concentrations in wintertime sea ice (Chukchi Sea, March 1999). When sea-ice horizons were exposed to wintertime temperatures of -5 to -25 C for 3-15 months, EPS concentrations increased significantly. Microscopic observations of frozen ice sections revealed a predominance of pennate diatoms, with intact and autofluorescent chloroplasts, sequestered in brine pockets 200 micrometers from interconnected veins. The relative dimensions of diatom-bearing brine pockets, frustule and chloroplast preservation in pennate diatoms, and indications of mucus in pockets containing the cells support the hypothesis that EPS can serve as cryoprotectants for diatoms during winter. A significant correlation between EPS concentration and bacterial abundance begs additional questions about the role of exopolymers in sea ice. Clearly, by arrival of spring, numerous sea-ice organisms were preserved during wintertime and high concentrations of EPS are available for release into seawater, contributing a previously unrecognized term to the polar carbon cycle.